Ionic barrier

Abstract

The invention features an electrochemical cell having two fluid-containing compartments separated by a nonselective microporous membrane. Select ions which would normally pass through the membrane under the influence of an ionic field, are prevented from passing through the membrane by a polyelectrolyte which has migrated through the compartment fluid to the membrane. The polyelectrolyte acts as an ionic barrier to the passage of select ions, thus effectively increasing the ion-selective capability of the membrane and, hence, the coulombic efficiency of the electrochemical cell.

What is claimed is: 
     
       1. An electrochemical cell, comprising: a first fluid-containing compartment;   a second fluid-containing compartment;   a nonselective porous membrane disposed between said first and second fluid-containing compartments;   means for passing ions through said membrane; and   a polyelectrolyte disposed in a fluid of at least one of said fluid-containing compartments for migrating towards, and forming an ionic barrier at, said membrane in response to the ionic flow through said membrane, said polyelectrolyte improving the efficiency of said cell by causing substantially only selected ions to pass through said membrane.   
     
     
       2. The electrochemical cell of claim 1, comprising a plurality of pairs of first and second fluid compartments, each pair of compartments being separated by a nonselective porous membrane, and wherein at least one of said compartments of each pair contains a polyelectrolyte. 
     
     
       3. The electrochemical cell of claim 1, wherein said cell is contained within a battery system. 
     
     
       4. The electrochemical cell of claim 1, wherein said cell is rechargeable. 
     
     
       5. The electrochemical cell of claim 1, wherein said cell is part of a zinc-bromine system. 
     
     
       6. The electrochemical cell of claim 1, wherein said polyelectrolyte is substantially negatively charged. 
     
     
       7. The electrochemical cell of claim 1, wherein said polyelectrolyte is substantially positively charged. 
     
     
       8. The electrochemical cell of claim 1, wherein said polyelectrolyte is amphoterically charged. 
     
     
       9. The electrochemical cell of claim 1, wherein said polyelectrolyte contains a sulfonated polystyrene. 
     
     
       10. The electrochemical cell of claim 1, wherein said polyelectrolyte contains a carboxylated polystyrene. 
     
     
       11. The electrochemical cell of claim 1, wherein said membrane is microporous. 
     
     
       12. The electrochemical cell of claim 1, wherein said membrane consists of polypropylene. 
     
     
       13. The electrochemical cell of claim 1, wherein said membrane consists of polystyrene. 
     
     
       14. The electrochemical cell of claim 1, wherein said membrane has an average pore size of between 0.005 to 0.30 microns. 
     
     
       15. The electrochemical cell of claim 14, wherein said membrane has an average pore size of between 0.1 to 0.6 microns. 
     
     
       16. The electrochemical cell of claim 1, wherein said membrane consists of a polymer. 
     
     
       17. The electrochemical cell of claim 1, wherein said membrane contains between 30 to 90% void space. 
     
     
       18. The electrochemical cell of claim 1, wherein at least one of said fluid-containing compartments includes means for circulating fluid. 
     
     
       19. An electrochemical cell, comprising: a first fluid-containing compartment;   a second fluid-containing compartment;   a third fluid-containing compartment;   a first nonselective porous membrane of a set disposed between said first and second fluid-containing compartments;   a second nonselective porous membrane of said set disposed between said second and third fluid-containing compartments;   means for passing ions through said membranes;   a polyelectrolyte disposed in a fluid of said second fluid-containing compartment, said polyelectrolyte improving the efficiency of said cell by causing substantially only selected ions to pass through said set of membranes.   
     
     
       20. The electrochemical cell of claim 19, comprising a plurality of sets of first, second and third fluid compartments, each compartment of a set being separated by a nonselective porous membrane, and wherein said second compartment of said set contains a polyelectrolyte. 
     
     
       21. The electrochemical cell of claim 19, wherein said cell is contained within a battery system. 
     
     
       22. The electrochemical cell of claim 19, wherein said cell is rechargeable. 
     
     
       23. The electrochemical cell of claim 19, wherein said cell is part of a zinc-bromine system. 
     
     
       24. The electrochemical cell of claim 19, wherein said polyelectrolyte is substantially negatively charged. 
     
     
       25. The electrochemical cell of claim 19, wherein said polyelectrolyte is substantially positively charged. 
     
     
       26. The electrochemical cell of claim 19, wherein said polyelectrolyte is amphoterically charged. 
     
     
       27. The electrochemical cell of claim 19, wherein said polyelectrolyte contains a sulfonated polystyrene. 
     
     
       28. The electrochemical cell of claim 19, wherein said polyelectrolyte contains a carboxylated polystyrene. 
     
     
       29. The electrochemical cell of claim 19, wherein said membranes are microporous. 
     
     
       30. The electrochemical cell of claim 19, wherein said membranes consist of polypropylene. 
     
     
       31. The electrochemical cell of claim 19, wherein said membranes consist of polystyrene. 
     
     
       32. The electrochemical cell of claim 19, wherein said membranes have an average pore size of between 0.005 and 0.30 microns. 
     
     
       33. The electrochemical cell of claim 32, wherein said membranes have an average pore size of between 0.01 to 0.06 microns. 
     
     
       34. The electrochemical cell of claim 19, wherein said membranes consist of a polymer. 
     
     
       35. The electrochemical cell of claim 19, wherein said membranes contain between 30 to 90% void space. 
     
     
       36. The electrochemical cell of claim 19, wherein at least one of said fluid-containing compartments includes means for circulating a fluid. 
     
     
       37. An ion-selective apparatus, comprising: a fluid containing ions;   means for establishing a flow of said ions in said fluid;   a polyelectrolyte disposed in said fluid and tending to migrate under the influence of said ionic flow; and   means disposed in said fluid for restraining said polyelectrolyte against migration in said fluid, whereby said polyelectrolyte will form an ionically selective barrier to certain ones of said ions in said fluid.   
     
     
       38. The ion-selective apparatus of claim 37, wherein said restraining means is a porous membrane which will pass the ions in said fluid, but which is nonporous with respect to said polyelectrolyte. 
     
     
       39. The ion-selective apparatus of claim 38, wherein said porous membrane has an average pore size of between 0.005 to 0.30 microns. 
     
     
       40. The ion-selective apparatus of claim 39, wherein said porous membrane has an average pore size between 0.0l to 0.06 microns. 
     
     
       41. The ion-selective apparatus of claim 38, wherein said membrane consists of a polymer. 
     
     
       42. The ion-selective apparatus of claim 38, wherein said membrane consists of polypropylene. 
     
     
       43. The ion-selective apparatus of claim 38, wherein said membrane consists of polystyrene. 
     
     
       44. The ion-selective apparatus of claim 38, wherein said membrane contains between 30 to 90% voids. 
     
     
       45. The ion-selective apparatus of claim 37, wherein said polyelectrolyte is substantially negatively charged. 
     
     
       46. The ion-selective apparatus of claim 37, wherein said polyelectrolyte is substantially positively charged. 
     
     
       47. The ion-selective apparatus electrochemical cell of claim 37, wherein said polyelectrolyte is amphoterically charged. 
     
     
       48. The ion-selective apparatus of claim 37, wherein said polyelectrolyte contains a sulfonated polystyrene. 
     
     
       49. The ion-selective apparatus of claim 37, wherein said polyelectrolyte contains a carboxylated polystyrene. 
     
     
       50. The ion-selective apparatus of claim 37 contained within a battery system. 
     
     
       51. The ion-selective apparatus of claim 50, wherein said battery system is rechargeable. 
     
     
       52. The ion-selective apparatus of claim 37, contained in a zinc-bromine system.